Fans are widely used appliances in industrial and service sector. They can be important components in production processes, and a failure of a fan system can cause significant production losses and hazards to worker safety. In addition to their importance in production processes, fan systems consume vast amounts of electrical energy. One sixth of the electricity consumed in electrical motors is consumed by fan systems in the industrial sector, and over one fourth in the service sector.
The use of frequency converters in the control of fan systems has become common, and will increase in the future, because of the efficiency benefits of rotational speed control. Frequency converters can also produce estimates of the state of the motor, including shaft mechanical torque and rotational speed, based on the motor model and internal current and voltage measurements. With the help of fan parameters provided by the fan manufacturers, these estimates can be used to determine the operating point of a fan (i.e., the produced flow rate and pressure).
Stalling phenomenon is one of the most common harmful events occurring in a fan, and it can reduce the service life and reliability of a fan. There is equipment available for reducing the risk of a fan stall, for example, by altering the upstream flow, but no known method for detecting a stall occurrence in a fan without the use of external measurements.